Since the discovery of ferrocene in 1951, a large number of metallocenes have been prepared by the combination of compounds prepared from cyclopentadienyl-type, indenyl-type, and fluorenyl-type compounds and various transition metals. Many of such metallocenes have been found useful in catalyst systems for the polymerization of olefins.
It has been noted that variations in the chemical structure of the metallocene can have significant effects upon the suitability of the metallocene as a polymerization catalyst. For example, the type, size and location of substituents on cyclopentadiene ligands have been found to affect the activity of the catalyst, the stereoselectivity of the catalyst, the stability of the catalyst, or various properties of the resulting polymer. However, the effects of various substituents is still largely an empirical matter; that is, experiments must be conducted in order to determine just what effect a particular variation in the chemical structure of the metallocene will have upon its behavior as a polymerization catalyst.
Among the cyclopentadienyl substituents that have been investigated are aminosilyl moieties, at least partly because of the potential for hydrolytic cleavage of the Si—N bond. Thus, for example, the paper entitled Synthesis of {1,3-bis(η5-tetramethylcyclopentadienyl)-1,1,3,3-tetramethyldisiloxane}dichlorotitanium (IV) via hydrolysis of bis {η5—(N,N-dimethylaminodimethylsilyl)tetramethylcyclopentadienyl} dichlorotitanium (IV) by Zemanek et al. in Inorganic Chemistry Communications 2001, 4(9), 520 discloses that bis {(N,N-dimethylaminodimethylsilyl) tetramethylcyclopentadienyl} titanium dichloride undergoes hydrolytic cleavage to produce TiCl2(C5Me4SiMe2)2O. In addition, the paper entitled Synthesis, Structure and Reactivity of Zirconocene Dichloride with (Me3Si)2 NSiMe2 Side Chains, by Rau et al. in European Journal of Inorganic Chemistry 2001, 1785 discloses the synthesis of the zirconocene [C5H4SiMe2N(SiMe3)2]ZrCl2.
U.S. Pat. No. 6,087,290 discloses a Si—N—Si bridged metallocene complex of the formula [L—SiMe2NRSiMe2L]MX2 wherein L is a C5H4, C9H6 or C13H8 radical; R is an alkyl radical selected from methyl, propyl, butyl, octyl, prop-2-enyl, 2-methoxyethanyl, 3-phenylethyl, 3-phenylpropanyl, and 4-phenylbutanyl.; M is selected from titanium, hafnium, and zirconium; and X is selected from chlorine, bromine, iodine, methyl and diethyl amine. The metallocene complex is produced by contacting a bidentate ligand precursor of the formula L—SiMe2—NHR with an equimolar amount of an organolithium compound of the formula RLi to form a single deprotonized ligand precursor of the formula Li[L—SiMe2—NHR], contacting the single deprotonized ligand precursor with half an equivalent of MX4 to produce a precursor complex of the formula (LSiMe2NHR)2MX2 and then contacting the precursor complex with another equivalent of MX4.
U.S. Pat. No. 6,630,549 discloses a a method of producing an olefin polymer by continuous slurry polymerization or continuous gaseous phase polymerization in the presence of a metallocene catalyst, exemplified by a compound of the formula:LjWkMXpX′qwherein L (each occurrence) independently represents an η-bonded, cyclic anionic ligand selected from the group consisting of a cyclopentadienyl group, an indenyl group, a tetrahydroindenyl group, a fluorenyl group, a tetrahydrofluorenyl group and an octahydrofluorenyl group, wherein the bonded, cyclic anionic ligand optionally has 1 to 8 substituents, each of which independently has up to 20 non-hydrogen atoms and is independently selected from the group consisting of a C1-C20 hydrocarbon group, a halogen, a C1-C12 halogen-substituted hydrocarbon group, a C1-C12 aminohydrocarbyl group, a C1-C12 hydrocarbyloxy group, a C1-C12 dihydrocarbylamino group, a C1-C12 hydrocarbylphosphino group, a silyl group, an aminosilyl group, a C1-C12 hydrocarbyloxysilyl group and a halosilyl group; M represents a transition metal selected from transition metals of Group 4 of the Periodic Table, each independently having a formal oxidation state of +2, +3 or +4, the transition metal being bonded, in a η5-bonding mode, to at least one L; W represents a divalent substituent having up to 50 non-hydrogen atoms, which has one valence bonded to L and one valence bonded to M, so that W, L and M together form a metallocycle; X (each occurrence) independently represents a ligand having up to 60 non-hydrogen atoms, which is a monovalent σ-bonded anionic ligand having both valences bonded to M, or a divalent σ-bonded anionic ligand having one valence bonded to M and one valence bonded to L; X′ (each occurrence) independently represents a neutral Lewis base ligating compound having up to 40 non-hydrocarbon atoms; j is 1 or 2, with the proviso that, when j is 2, two L ligands are optionally bonded together through a divalent group having up to 20 non-hydrogen atoms, which is selected from the group consisting of a C1-C20 hydrocarbadiyl group, a C1-C12 halohydrocarbadiyl group, a C1-C12 hydrocarbyleneoxy group, a C1-C12 hydrocarbyleneamino group, a siladiyl group, a halosiladiyl group and an aminosilane; k is 0 or 1; p is 0, 1 or 2, with the proviso that when X is a monovalent σ-bonded anionic ligand or a divalent σ-bonded anionic ligand having one valence bonded to M and one valence bonded to L, p is an integer which is one or more smaller than the formal oxidation state of M, and that, when X is a divalent σ-bonded anionic ligand having both valences bonded to M, p is an integer which is (j+1) or more smaller than the formal oxidation state of M; and q is 0, 1 or 2.